A steering apparatus that has a rack and pinion steering gear unit that uses a rack and pinion as a mechanism for converting rotating movement that is inputted from the steering wheel to linear movement for applying a steering angle is widely known. Moreover, a rack and pinion steering gear unit can be made compact and lightweight, and high rigidity and good steering feeling can be obtained, so is widely used.
FIG. 28 to FIG. 30 illustrates construction that was disclosed in JP2012-51406 (A) as an example of a steering apparatus in which this kind of rack and pinion steering gear unit is assembled. In this steering apparatus, movement of a steering shaft 2 that is rotated by operating a steering wheel 1 is transmitted to a pinion shaft 6, which is an input shaft of a steering unit 5, by way of a pair of universal joints 3 and an intermediate shaft 4.
The steering gear unit 5 is achieved by pinion teeth 7 that are provided on the tip end half of a pinion shaft 6 engaging with rack teeth 9 that are provided on the front surface of a rack shaft 8. Part of both the pinion shaft 6 and rack shaft 8 are housed inside a casing 10. The casing 10 has a cylindrical shaped main housing section 11 and a cylindrical shaped sub housing section 12. Of these, the main housing section 11 is open on both ends. The sub housing section 12 is provided on one side of the main housing section 11, and one end is open. The center axis of the main housing section 11 and the center axis of the sub housing section 12 are in a twisted positional relationship with each other. The rack shaft 8 is inserted through the main housing section 11 so as to be able to displace in the axial direction, and both end sections of the rack shaft 8 protrude from the main housing section 11. The base end sections of tie rods 14 are linked with both end sections of the rack shaft 8 by way of spherical joints 13. The tip end sections of these tie rods 14 are linked to the tip end sections of knuckle arms (not illustrated in the figure) by pivot shafts. By the pinion teeth 7 engaging with the rack teeth 9, the rack shaft 8 does not rotate around the center axis of the rack shaft 8 itself.
The pinion shaft 6 is such that the tip-end half where the pinion teeth 7 are formed is supported inside the sub housing section 12 so as to be able to rotate. In order for this, the tip-end section of the pinion shaft 6 is supported in the rear-end section of the sub housing section 12 by a radial needle bearing 15 so as to be able to freely rotate. Moreover, the middle section of the pinion shaft 6 is supported in the portion near the opening of the sub housing section 12 by a single-row ball bearing 16. The inner ring 17 of the ball bearing 16 is held between a radially inside stepped surface 19 that is formed around the middle section of the pinion shaft 6 and a conical shaped retaining ring 20 that engages with the middle section of the pinion shaft 6. The outer ring 18 of the ball bearing 16 is held between a radially outside stepped surface 21 that is formed around the middle section of the inner circumferential surface of the sub housing section 12 and a pressure screw cylinder 22 that is screwed into the inside of the end section on the opening side of the sub housing section 12. With this construction, the tip end half section of the pinion shaft 6 is supported inside the sub housing section 12 so as to be able to support both a radial load and a thrust load, and so as to be able to rotate while preventing displacement in the axial direction thereof.
Moreover, a cylinder section 23 is provided on the portion of the opposite side in the radial direction of the main housing section 11 from the sub housing section 12. A sliding block 25 that supports a pressure roller 24 so as to be able to rotate freely is housed inside this cylinder 23 so as to be able to move in the axial direction. A spring 27 is provided between a cover 26 that is fastened to the inside of the end section on the opening side of the cylinder 23 by a screw and the pressure block 25, and that spring 27 presses the pressure roller 24 toward the rack shaft 8. As a result, the rack shaft 8 is elastically pressed toward the pinion shaft 6, which eliminates looseness in the engagement section between the pinion teeth 7 and the rack teeth 9. Moreover, regardless of a force applied to the rack shaft 8 in the direction going away from the pinion shaft 6 that is caused by the transmission of power in the engagement section, it is possible to properly maintain a state of engagement in this engagement section.
When applying a steering angle to the left and right front wheels, the pinion shaft 6 is rotated by operating the steering wheel 1. In doing so, pinion teeth 7 and the rack teeth 9 engage, the rack shaft 8 displaces in the axial direction, and the pair of tie rods 14 that are linked to both end sections of the rack shaft 8 are pushed or pulled. As a result, the desired steering angle is applied to the left and right front wheels.
In the case of a steering gear unit 5 of a first example of conventional construction having this kind of construction, the pressure screw cylinder 22 is used to apply a preload to the ball bearing 16 that supports the pinion shaft 6. As a result, even though a force is applied to the pinion shaft 6 during steering, the engaged state of the engagement section between the pinion teeth 7 and rack teeth 9 is kept stable by preventing displacement of the pinion shaft 6 in the radial direction (left-right direction in FIG. 30) and in the thrust direction (up-down direction in FIG. 30). Moreover, together with suppressing the occurrence of striking noise between teeth in this engagement section, fluctuation of the steering force is prevented. By using the pressure screw cylinder 22 in this way, it becomes easy to apply a necessary preload to the ball bearing 16, and it is possible to effectively prevent the ball bearing 16 from displacing in the axial direction. However, when using the pressure screw cylinder 22, the installation space increases, so it becomes easy for the overall length of the sub housing section 12 to become long and for the steering gear unit 5 to become large. There is also a problem in that the work time for adjusting the preload becomes long.
JP2010-195278 (A) discloses construction where, instead of this kind of pressure screw cylinder, an incomplete circular shaped retaining ring is used to prevent a rolling bearing from falling out while applying a preload to the rolling bearing. FIG. 31 illustrates a steering gear unit 5a of a second example of conventional construction as disclosed in JP2010-195278 (A). In the case of this steering gear unit 5a, a fastening groove 28 is formed around the entire circumference of the portion near the opening of the inner-circumferential surface of a sub housing section 12a of a casing 10a. With the radially outside portion of an incomplete circular shaped retaining ring (tapered snap ring) 29 fastened in this fastening groove 28, one side surface in the axial direction of the radially inside portion of this retaining ring 29 is pressed against the side surface in the axial direction of an outer ring 18 of a ball bearing 16 that supports the middle section of a pinion shaft 6 so as to be able to rotate freely.
Moreover, the side surface 30 of the fastening groove 28 on the opening side (top side in FIG. 31) of the sub housing section 12a is inclined in a direction such that the width of the fastening groove 28 expands toward the inside in the radial direction. A tapered surface 31 is also formed in the portion of the retaining ring 29 that comes in contact with the side surface 30, and the cross-sectional shape of the radially outside portion of this retaining ring 29 is a wedge shape that is inclined in a direction such that the thickness dimension in the axial direction becomes smaller toward the outside in the radial direction. In the case of this kind of construction, the installation space of the retaining ring 29 is small, so it becomes easier to make the steering gear unit 5a more compact. Moreover, the work time for assembling the retaining ring 29 is short and does not require adjusting a preload.
However, when a force is applied to the pinion shaft 6 during steering, a thrust force acts on the retaining ring 29 in the upward direction in FIG. 31, which causes the diameter of the retaining ring 29 to contract being guided by the side surface 30, and it becomes easy for the retaining ring 29 to displace in the axial direction. As a result, it becomes easy for the ball bearing 16 to displace in the axial direction, and there is a possibility that occur such as shifting of the engagement section between the pinion teeth 7 and the rack teeth 9 from the proper position, the occurrence of noise, and fluctuation of the steering force.
In consideration of a situation such as described above, JP2010-38254 (A) discloses construction in which, even though a force is applied to the pinion shaft during steering, it is possible to prevent contraction of the retaining ring. FIG. 32 illustrates a steering gear unit 5b of a third example of conventional construction that is disclosed in JP2010-38254 (A). In the case of this steering gear unit 5b, plural protrusions 32 that protrude in the axial direction are formed on the outer peripheral edge of a tapered surface 31a of a retaining ring 29a. Moreover, an annular concave groove 33 is formed in a side surface 30a of a fastening groove 28a that is formed around the inner circumferential surface of a sub housing section 12b of a casing 10b. With the radially outside portion of the retaining ring 29a fastened in the fastening groove 28a, the protrusions 32 are located inside the annular concave groove 33.
Therefore, even when a thrust force acts on the retaining ring 29a in the upward direction in FIG. 32 when a force is applied to the pinion shaft 6 during steering, the protrusions 32 engage with the annular concave groove 33 and prevent contraction of the diameter of the retaining ring 29a. Therefore, it becomes difficult for the retaining ring 29a to displace in the axial direction, and it is possible to suppress the ball bearing 16 from displacing in the axial direction and to properly maintain the engagement position of the pinion teeth and rack teeth. However, the shapes of the fastening groove 28a and the retaining ring 29a are complicated, so there is a problem in that the processing becomes troublesome and the manufacturing cost increases.